1. Field of the Invention
The present invention relates to a semiconductor laser diode (hereafter denoted as LD) with a ridge waveguide structure, and a method to manufacture the LD.
2. Related Prior Art
In an LD with the ridge waveguide structure, the active layer accompanied with optical confinement layers extends in a plane, but a waveguide with a striped structure extending in one direction within the plane is formed above the laterally extending active layer, and the ridge waveguide made of semiconductor materials is buried with the burying layer. The United States Patent published as US 20090141764A or Aoki et al. in IEEE Quantum Electronics, vol. QE-3(2), (1997), pp. 672 have disclosed one type of the LD with the ridge waveguide structure with a burying layer made of resin. This resin layer extends from one facet of the LD to the other facet. In such an LD, semiconductor materials including the burying layer to bury the ridge waveguide structure are put between two electrodes. This arrangement equivalently forms a parallel plate capacitor. In order to operate the LD in quite high speed, for instance, over 10 Gbps, not only the junction capacitance but the parasitic capacitance must be reduces as possible. One solution is that an area of the upper electrode provided on the burying layer is narrowed. The LDs disclosed in the prior arts above set the burying layer thick enough to reduce the parallel plate capacitance.